This invention relates to a method and apparatus for conserving energy in appliances which utilize a flow of hot water for cleaning purposes such as shower baths.
It has been reported that approximately 4 percent of the total national consumption of fuel in the United States is used to heat hot water in commercial and residential buildings. Of this amount, approximately one-fourth, or 1 percent of the total is used to heat bath water, mostly for shower bathing purposes. At the present rate of consumption of fuels in the United States, approximately 80.times.10.sup.15 BTU per year, shower bathing in residences may consume approximately 0.8.times.10.sup.15 BTU: the equivalent of about 1.6 hundred million barrels of oil per year. Thus, the conservation of energy in shower bathing is of large potential significance.
Conventional shower baths comprise a bathing compartment fitted with a nozzle, a mixing valve, and a drain. Hot water, typically from a central boiler installed in the building in which the shower bath is located, and cold water are fed into the mixing valve and are there combined to form a stream of water which exits the nozzle at a selected bath water temperature intermediate that of the cold and hot water inputs. In an open shower stall, a substantial fraction of the heat contained in the bath water exiting the nozzle will be lost by ongoing evaporation with the result that the water entering the drain will be at a lower temperature. However, in an enclosed bathing compartment equipped with a shower door, the interior of the compartment quickly becomes saturated with water vapor. This results in a drain water temperature substantially equal to the temperature of the water exiting the nozzle.
From the foregoing it is apparent that a certain amount of energy could be conserved in shower bathing if the warmed drain water could be passed in heat exchange relation with cold water. This would result in a warmer cold water input, and less hot water would be needed to attain a selected bathing water temperature. This broad concept is known to the art as evidenced, for example, by West German Offenlegungsschrift No. 24 47 428 (Apr. 17, 1975).